SAN FRANCISCO — Although it looks increasingly unlikely that NASA will launch a flagship mission to Jupiter during the next decade, the upcoming Juno mission may provide scientists with some unexpected opportunities to study the gas giant’s moons.
“Once you have a NASA satellite in orbit, you want to take the opportunity to gather as much information as you can,” said Scott Bolton, Juno principal investigator and director of the space science and engineering division at the Southwest Research Institute in San Antonio.
The solar-powered Juno mission, which was conceived as a carefully targeted exploration of Jupiter’s formation and composition, is scheduled to begin its five-year journey in August. While the mission will remain focused on its primary goals, its instruments may provide scientists with data they can use to study Jupiter’s moons, including Europa, which has attracted widespread interest because it may harbor large quantities of water.
A NASA-led mission to Europa, once considered a leading contender for future funding, now appears unlikely to occur as conceived in light of budget pressures that may cap the space agency’s contribution to any flagship-class planetary probe at $1 billion. Jim Green, director of NASA’s Planetary Science Division, mentioned that cost cap March 3 in comments to the NASA Advisory Council’s Science Committee.
A recent report by the National Research Council cites missions to Mars to gather rocks and a trip to Europa as the top-priority destinations for planetary exploration in the next decade. The report, which urges NASA to trim mission costs, said the Jupiter Europa Orbiter project would cost $4.7 billion while the Mars sample return mission would cost $3.5 billion. Green told the committee that the space agency is not likely to conduct those missions in the near future unless international partners contribute a significant amount of the funding required. The White House budget proposal sent to Congress in February calls for planetary spending to decline from $1.54 billion in 2012 to $1.25 billion in 2016.
Still, NASA’s decision on future missions will not have a significant impact on Juno. The spacecraft and its instruments have been built and tested in preparation for launch, Bolton said. The science campaign as well as the path the spinning spacecraft will travel in its orbit has been carefully designed to pass through specific longitudes to produce a complete map of Jupiter’s gravity and magnetic fields, he added.
Studying Jupiter’s moons is not a key objective of the project, but the science team will use the spacecraft’s infrared, ultraviolet and visible cameras to gather imagery. “We were already planning to do that,” Bolton said. The spacecraft’s polar orbit will give scientists a unique vantage point, he added.
Juno was selected in 2008 as part of NASA’s New Frontiers series of medium-class spacecraft. Unlike flagship missions, which are designed to conduct far-reaching research campaigns, New Frontiers missions are targeted science campaigns. The Juno spacecraft, built by Lockheed Martin Space Systems of Denver, is equipped with a suite of nine instruments to examine the jovian atmosphere, study the planetary core, measure the strength and direction of Jupiter’s magnetic field, and view the auroras produced by charged particles in Jupiter’s atmosphere. NASA’s Jet Propulsion Laboratory in Pasadena, Calif., manages the mission.
Scheduled for launch on Aug. 5 from Cape Canaveral, Fla., aboard a United Launch Alliance Atlas 5 rocket, the Juno mission entails a five-year trip through the solar system to arrive in Jupiter’s orbit in July 2016. Once there, the spacecraft is expected to make 33 trips around the planet in a highly elliptical polar orbit before allowing itself to be pulled into the planet’s atmosphere, where it will crush and burn in October 2017, Bolton said.
If the spacecraft and its instruments continue to work well as it approaches the end of its anticipated life, the mission could be extended. “Certainly there would be an opportunity to continue flying the spacecraft,” said Tim Gasparrini, Lockheed Martin’s Juno program manager.
However, the spacecraft is expected to be subjected to such high levels of radiation during its travels in the jovian atmosphere that it probably would not be able to continue flying much longer than planned, Bolton said.
Juno’s orbit is designed to avoid Jupiter’s radiation belts for as long as possible to protect instruments and electronics from the damaging effects of radiation. “We rapidly accumulate radiation at the end of the mission,” Gasparrini said. “We get half of our radiation exposure after orbit 26.”
While Lockheed Martin engineers have never before designed a spacecraft destined for Jupiter, Juno draws on hardware and software from previous missions. The avionics suite, for example, is similar to the flight hardware and software developed for the company’s Mars Reconnaissance Orbiter, Gasparrini said. Engineers augmented that design with a titanium vault to protect sensitive electronic components from radiation, he added.
Traveling to Jupiter presents other challenges as well. To prevent the charged particles in Jupiter’s atmosphere from accumulating on the spacecraft’s exterior and then discharging, the entire surface had to be built with conductive materials. In addition, Juno’s reliance on solar power to travel more than 644 million kilometers from the sun required engineers to equip the satellite with three highly efficient solar panels, which each measure 8 to 9 meters in length. Those solar panels, which provide 18 kilowatts of power above Earth’s atmosphere, will provide only 400 watts in Jupiter’s orbit, Gasparrini said.
In 2005, when NASA announced plans to send a scientific probe to Jupiter as part of the New Frontiers program, the agency imposed a $700 million cost cap on the mission. Due to budget constraints, space agency officials delayed the mission’s scheduled launch from 2009 to 2011. Those delays plus accounting changes raised Juno’s overall cost. In a report released in March, the U.S. Government Accountability Office set a $1.1 billion price on the Juno mission.
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